The present invention is directed broadly to an improved fluid vaporizing apparatus and method for producing a gas-phase mixture.
The present invention is directed more specifically to an improved fuel vaporizing system and associated process for producing a vaporized chemically-stoichiometric gas-phase fuel-air mixture for use in internal combustion engines.
In the context of this document the terms "Vaporize", "Vaporizing", "Vaporized" or any derivative thereof means to convert a liquid from an aerosol or vapor-phase to a gas-phase by means of vorticular turbulence.
Internal combustion engines (both diesel and otto-cycle gasoline) currently employ various systems for supplying a fuel aerosol of liquid fuel droplets and air, either directly into the diesel engine combustion chamber where compression heat ignites the fuel-air mixture or with a carburetor or fuel injection device(s) through an intake manifold into an otto-cycle engine combustion chamber where an electric spark ignites the mixture of air and fuel vapor, which is produced as the smaller aerosol droplets vaporize. In all currently employed systems this fuel-air mixture is produced by atomizing a liquid fuel and supplying it as a fuel aerosol into an air stream. But, in order for fuel oxidation within the combustion chamber to be chemically complete, the fuel-air aerosol must be vaporized to a chemically-stoichiometric gas-phase mixture. Stoichiometricity is a condition where the amount of oxygen required to completely burn a given amount of fuel is supplied in a homogeneous mixture resulting in optimally correct combustion, with no residues remaining from incomplete or inefficient oxidation. Ideally, the fuel aerosol should be completely vaporized, intermixed with air and homogenized PRIOR to entering the combustion chamber. Aerosol fuel droplets do not ignite and combust completely in any current type of internal combustion engine.
As a result, unburned fuel residues are exhausted from the engine as pollutants such as hydrocarbons (HC), carbon monoxide (CO), and aldehydes, with concomitant production of oxides of nitrogen (NOx). These residues require further treatment in a catalytic converter(s) to meet current emission standards and result in additional fuel costs to operate the catalytic converter(s). A significant reduction in any or all of these pollutants and the required control hardware would be highly beneficial, both economically and environmentally.
Moreover, a fuel-air mixture that is not completely vaporized and chemically-stoichiometric results in incomplete combustion, causing the internal combustion engine to perform inefficiently. Since a smaller portion of the fuel's chemical energy is converted to mechanical energy, fuel energy is wasted, thereby generating unnecessary heat and pollution.
The mandate to reduce air pollution has necessitated attempts to correct or compensate for combustion inefficiencies with a multiplicity of fuel system and internal-engine modifications and also add-ons. These various external control devices are all intended to more completely vaporize-homogenize fuel-air mixtures. As evidenced in the prior art concerning fuel preparation systems, much effort has been expended to reduce the aerosol droplet size and increase system turbulence while providing sufficient heat and enough residence time to evaporate-vaporize the fuels to allow complete combustion. However, the achievement of total aerosol vaporization has proven difficult because current liquid hydrocarbon fuels, such as gasoline, are mixtures composed of numerous "tray fractions" from the oil refinery fractionating tower. The lighter and more volatile fuel fractions vaporize and combust when the fuel is subjected to combustion heat with in-cylinder heat-turbulation. Heavier and less volatile components require additional kinetic energy and cylinder residence time to obtain sufficient molecular agitation and particle size-weight reduction for vaporization. As evidenced by the present internal combustion engine pollution emissions, these problems have been moderated but never solved.
As paradoxical as it may seem, the present problems of engine inefficiency and resultant harmful emissions exist because of a "misdirection" or "mistake" in the early days of combustion engine development. The first gasoline engines used a simple device that included a series of fuel saturated cloth wicks, or panels, through which the air was drawn into the intake manifold by engine vacuum. As the air moved past or through the wicks, the gasoline vapors were drawn into high compression ratio engine cylinder(s). Combustion was then initiated by means of a very crude live flame or electric spark ignition system. This fuel-air mixture was in fact a very combustible and efficient vapor-phase. The problem developed because as the more volatile fuel molecules were removed from the gasoline, the fluid left behind in the tank became less and less volatile and heavier in specific gravity until the engine would not satisfactorily operate. This system left a troublesome, heavy, non-volatile, oily residue which was totally unsuitable as a spark ignition-otto-cycle engine fuel, and which then had to be drained from the fuel tank and discarded. When the tank was resupplied with fresh gasoline, the engine would again run and the process was started over.
The solution was ingeniously simple, BUT WRONG, and involved dripping fresh fuel taken from the bottom of the fuel tank into the engine inlet air stream, thus creating a FUEL AEROSOL MIXTURE, which could only be utilized in very low-compression ratio gasoline engines because of detonation problems. Continued aerosol fuel system developments produced the up-draft venturi otto-cycle type carburetion devices and the diesel cycle compression ignition engine. Next followed mechanical fuel pumps to feed down draft carburetors with single, then multiple throats, and more recently, the many variations and improved types of direct and indirect fuel injectors for both gasoline and diesel engines which all produce fuel aerosols.
This sequential series of developments covers approximately 100 years, with every significant improvement directed at creating a more effective fuel aerosol. Today, both diesel injection and otto-cycle gasoline fuel systems continue to create at best inefficient fuel aerosols. These aerosols contain both gas vapor and liquid fuel droplets, which droplets generate power only if the droplets can be heat vaporized and burned during the combustion "cycle" time in the engine combustion chamber. Due to the carbon particulates resulting from this process, the combustion that occurs is termed "luminous flame combustion" and is incomplete. As a result, otto-cycle gasoline internal combustion engines utilizing aerosol fuel systems are severely limited by specific fuel combustion characteristics, fuel type and grades, and cannot employ high compression ratios (20:1 or above) because of detonation "knock." Moreover, this luminous flame combustion from aerosol fuels occurs above 2800.degree. F. and inherently causes NOx (oxides of nitrogen) to form in both diesel and gasoline engines.
In hindsight, fuel system development over the last 100 years has followed an inefficient but effective path. High combustion temperatures and inefficient initial fuel preparation result in high amounts of emission pollutants, which then require some type of control elements. The control elements currently in use, in the form of exhaust gas recirculation, camshaft modifications, retarded timing, lowered compression ratios, catalytic converters, air injection reactors, etc. have all compounded engine inefficiency. Total and complete fuel vaporization would allow the actual achievement of stoichiometric fuel oxidation to CO2 and H2O with significant improvements in pollution emissions. However, the current path being followed to solve the pollution-emissions problem appears to be directed at following the technologically difficult route(s) of specialized fuels, electric vehicles, exotic batteries, etc.
One solution to the above dilemma is the use of technology which actually does achieve stoichiometric fuel/oxidizer proportions as a combustion reality. The key is to reduce the fuel aerosol droplet size close to the molecular level so that complete (or nearly complete) vaporization to the gas phase occurs within the existing time, temperature and turbulence constraints of the fuel preparation system PRIOR to fuel-air mixture entry into the combustion chamber.
There have been attempts in the prior art, which have relied on a turbulent circulation of the fuel-air mixture to separate the unvaporized portion of the fuel-air mixture from the vaporized portion and to provide only the vaporized portion of the fuel-air mixture to the intake manifold of an internal combustion engine.
For example, the separator patented by Edmonson, U.S. Pat. No. 1,036,812, uses a heated spiral-shaped conduit 9 to help volatilize the liquid hydrocarbon passing through the conduit. In addition, the conduit subjects the liquid hydrocarbon to centrifugal action to throw the heavier-unvolatilized hydrocarbon particles against a perforated plate 15 to break up the particles or to pass the heavier particles through perforations 16 and thereby return the heavier particles to the conduit.
A device disclosed by Cox in U.S. Pat. No. 2,633,836, is interposed between the intake manifold inlet and the carburetor outlet to both separate liquid fuel (in the form of suspended or entrained droplets), from the fuel-air mixture flowing from the carburetor and to vaporize a portion of the liquid fuel. The separating or further vaporizing functions are accomplished by passing the fuel-air mixture through spiral passages or conduits that divide the flow of the fuel-air mixture. The passages or conduits impart a centrifugal or swirling force on the fuel-air mixture, causing fuel droplets to be deposited on the side walls of the conduits/passages, from which walls the droplets are drained and returned to the fuel line.
Another device, in the form of a carburetor, was disclosed by Dempsey in U.S. Pat. No. 4,715,346. This carburetor includes three mixing chambers 12, 14, 16 arranged vertically in tandem. Gasoline spray and air enter the outer chamber of top chamber 12 through slot 60, flow spirally toward the central portion of the top chamber, enter the intermediate chamber 14 at its central portion, flow spirally outwardly toward the outer portion of the intermediate chamber, enter the bottom chamber 16 at its outer portion, flow spirally toward the central portion 90 of the bottom chamber and exit into the manifold of an engine. Heavy aerosol particles are separated from the fuel-air mixture at the central portion of the first chamber, collected in a reservoir 71, passed through a heater 104, and fed back into the fuel-air mixture at the center of the intermediate chamber 14.
These prior art devices and processes are ineffective to produce total vaporization of the fuel. Moreover, the prior art devices and processes do not produce a "complete" homogeneous intermixing of the fuel vapor with combustion air.
On the other hand, the device patented by Rock et al., U.S. Pat. Nos. 4,515,734 and 4,568,500 (the same inventors as for the present invention) provides vaporized fuel to the intake manifold of an engine. Rock et al. described a series of mixing sites, including a venturi housing 172 for homogenizing and vaporizing fuel and air. The mixture passes tangentially into a fuel separating cyclone housing 190. In use, the fuel and air mixture entering the housing 190 circulates vortically at high speeds within an annular chamber 334. Any remaining non-vaporized or larger particles of fuel are impacted centrifugally against the interior surfaces of the walls 302 and 310, accumulated, and caused to flow by the force of gravity via a fuel return chute 336 to one of said mixing sites to be recycled into the venturi housing. A fully vaporized and homogeneous fuel-air mixture, absent any large particles of fuel, spills over the top edge 326 into the barrel 320 of the housing 190 and thence, into the intake manifold of an internal combustion engine. Essentially, only partially vaporized fuel reaches the cylinders of the engine.
The Rock et al. device provides important advantages in the operation of an internal combustion engine by cyclonically recycling non-vaporized particles of fuel, allowing almost total burning of all hydrocarbons in an associated engine. Nevertheless, there is a problem with the Rock et al. device in that the fuel-air mixture reaching the fuel-separating housing 190 contains too many non-vaporized particles of fuel, which should be recycled. The device only utilizes one mixing site to process the recycle fuel, which often leads to overloading the recycle system with resultant engine detonation from introducing aerosols into the engine combustion process. As a result, the device is not useful in an internal combustion engine having a compression ratio higher than standard production vehicles. It would be very advantageous if the device could be improved so that the fuel-air mixture could be completely vaporized to a gas-phase prior to entering the housing 190.